Potent Bronchodilating Effects of Enprofylline and Theophylline on Contractions Induced by Egg Albumin or by Slow Reacting Substance (SRS)

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Abstract
Isolated sensitized guinea pig tracheal smooth muscle tone was induced by use of egg albumin or SRS-A (slow reacting substance of anaphylaxis). The dose-response relationships of theophylline and enprofylline were studied on these preparations. Enprofylline was more potent than theophylline in relaxing the egg albumin- or SRS-A-induced tracheal muscle tone. The theophylline relaxation-curve was significantly shifted to the left after addition of adenosine-deaminase to the egg albumin-contracted trachea, but this was not observed with the enprofylline relaxation-curve. In SRS-A-contracted tracheas, the addition of adenosine-deaminase did not significantly alter the relaxation curves of theophylline or enprofylline. It is therefore suggested that the relaxing effects of theophylline and enprofylline on SRS-A-induced contractions, at the therapeutically relevant concentrations demonstrated in this study, might be of importance for the antiasthmatic effects of xanthines.